This invention relates to cutting or grooving of elastomers and like materials. More particularly, this invention relates to a cutting blade for resistance-heated cutters that allows for more efficient and better quality cutting.
It is known that resistance-heated cutters are widely used for cutting and grooving elastomers such as rubber. In a resistance-heated cutting process, electrical current from an external source is conducted through an electrically conductive cutting blade. Heat is generated in the cutting blade as an effect of resistance to electrical current flow.
Conventionally known electrically heated cutting blades, such as used in electrically heated tire groovers, are composed of a strip of electrically conductive material formed in a U-shape. In such prior art devices, the heat is not concentrated in the cutting edge of the blade, where it would be most effective in aiding the cutting of the material. Rather, just the opposite occurs during the cutting process, the cutting edge is cooled by the material being cut, and is the coolest part of the blade. Therefore, when sufficient heat is developed to maintain a favorable cutting edge temperature for optimum cutting performance, substantial excess heat is developed in the portions of the blade further from the cutting edge. This overheating causes severe damage and tends to reduce the life of the blade. The replacement of the burnt-out or heat damaged cutting blades is expensive and time consuming. The heat developed in portions of blade further away from the cutting edge also reduces the quality of cuts or grooves, produces undesired smoke by burning the elastomer, and transfers heat to other parts of the cutting assembly.
Thus, in Van Alstine, U.S. Pat. No. 4,797,999, there is disclosed a cutting head member allowing for rapid replacement means of the damaged cutting blades. This invention, however, does not address the problem of overheating of the parts of the blade away from the cutting edge.
In Wenger, U.S. Pat. No. 4,539,467, an electrically heated cutting tool is disclosed with means of airstream cooling of the parts of the blade away from the cutting region to reduce heat transfer to the blade holder and increase heat concentration in the cutting portion of the blade. Wenger's invention does not stop overheating of the blade, but only remedies it with cooling. Wenger also presents the disadvantage of requiring air supply means and is not energy efficient because a significant portion of heat energy is lost to the cooling system.
Another similar invention is disclosed in Lejuene, U.S. Pat. No. 3,850,222, where in order to concentrate thermal energy in the cutting zone, the cutting portion of the blade has a width that is significantly less than the width of the fastening zone so that the heating is greater in the cutting zone than fastening zone. Although this invention provides for means to concentrate the thermal energy in the cutting zone of the blade, the heat is not concentrated in the cutting edge of the blade. Therefore, the previously mentioned problems involved with overheating of the portions of the blade further away from the cutting edge are still likely to occur.